Aviation turbine fuels



.F. for relatively substantial time intervals.

aviation turbine fuel is subjected to even higher temperair vStates Patent ()fiiC 3,048,480 AVIATHON T t FUELS Arthur V. Churchill, Oalrmont, Pan, assignor to Gulf Research & Development Company, Pittsburgh, Pa a corporation of Delaware No Drawing. Filed June 9, 1959, Ser. No. 819,015

SClaims. (Cl. 44- -73) ing medium, or heat sink in combustion gas turbine powered aircraft to remove heat from lubricating oil that has absorbed heat developed in the engine by the compression of combustion air, by fuel combustion, and by friction of moving parts. As a result the fuel is subjected to service temperatures of the order of 300 to 400 In addition,

tures, of the order of 500 F for short periods of time in the area of the nozzles or orifices from which the fuel is introduced into the combustion chamber of the engine. As a result, certain components of the fuel tend to under- Ego decompositiondue to polymerization, oxidation, and

thermal decomposition, and to form solid or semi-solid.

degradation products that clog the fuel orifices and thereby interfere with proper combustion of the fuel. Ordinary stabilizing agents, antioxidants, and the like of the kind that a e employed to stabilize the fuels during storage have been found inadequate to inhibit deterioration of the fuels at the high service temperatures encountered in aviation turbine engines.

. y The use of high molecular weight 1,2,3-substituted 1,3- diones has been proposed to improve the thermal stability the combustion zone and in the heat-exchange section of the fuel supply system of an aviation turbine engine can be substantially improved by incorporation in the fuel of a small amount of a combination of (a) an N,N'-di- (orthohydroxyarylmethylidene)alkylenepolyamine that contains 2 to 3 amino groups and whose alkylene groups .contain 2 to 6 carbon atoms each, and (b) a beta-diketone havingthe general formula:

o H o 7 R-ii-hj-ii- -omm :where R is an aromatic hydrocarbongroup' having a nuclear carbon atom thereof connected directly to the adjacent carbonyl carbon atom and containing 6 to 22 carbon atoms, and R and R are like or unlike openchain saturated or unsaturated aliphatic hydrocarbon radi tetradecanedione.

v.rnetals may have upon the oils.

ferred, but 7 orthohydroxyarylmethylidene-substituted al- 'kylenepolyamines that are substituted with other groups such as alkoxy, halo, cyano and carboxy can be used. An example of a particularly outstanding orthohydroxyarylmethylidene-substituted alkylenepolyamine for the pur- 'poses of this invention is N,N-disalicylidene-1,2-propylenediamine. Examples of other N,N'-(orthohydroxyarylmethylidene)alkylenepolyarnines are N,N-di(2-hy droxy-6-methylbenzylidene) 2,3-butylenediamine, N,N- di(orthohydroxynaphthylidene) 1,3 propylenediarnine, N,N'-di(2-hydroxy 3 methoxybenzylidene) 3,4 diaminohexane, N,N'-di(2 hydroxy-S-chlorobenzylidene)- 1,2-propylenediamine, N,N'-di(2 hydroxy 3 cyanobenzylidene)ethylenediamine, N,N' di(2-hydroxy-3-car boxylbenzylidene)ethylenediamine and N,N'-disalicylidenediethylenetriamine. Beta-diketones having the formula indicated above where R is a mononuclear aromatic radical containing 6 to 12 carbon atoms, such as phenyl, tolyl, xylyl, and isobutylphenyl, R and R" are aryl groups containing 12 to 18 carbon atoms, such as octadecyl, hexadecenyl, and hexadecadienyl are preferred, but betadiketones where R is some other aromatic hydrocarbon snbstituent and where R and R are other acyclic hydrocarbon radicals can be used. Especially good results are obtainable when the beta-diketone is l-phenyl-Z-hexadecyl-l,3-eicosanedione. Examples of other 1,2,3-substituted 1,3-diones are 1-tolyl-2-octyl-1,3-hexadecanedione, l-xylyl-Z-decyl 1,3 tetradecanedione, 1 tolyl-2-decyl- 1,3-hexadecanedione, and l-tolyl-2-hexadecadienyl-1,3

The N,N-di(orthohydroxyarylmethylidene)alkylenepolyamines and the 1,2,3-substituted 1,3- diones disclosed herein can be employed in varying proportions With respect to one another. It is generally preferred to add them to aviation turbine fuels in about equal proportions by weight, but other proportions can be used provided the compound present in the smaller amount is present in an amount corresponding to at least about five pounds per thousand barrels of fuel.

ratios, for example 1:10 to 10:1, can be used.

- The exact mechanism by which the compounds disclosed herein function to improve the thermal stability of aviation turbine fuels has not been definitely established. It may be that the respective compounds tend to form stable complexes with traces of metals in the fuels that normally tend to catalyze high temperature instability, thereby inhibiting any catalytic effect such This possibility might seem to be borne out by the fact that both beta-diketones of-the class disclosed herein, that is, beta-diketones that contain high formula weight substituents in the 'l, 2, and 3 positions, as well as N,N-di(orthohydroxyarylmethylidene)alkylenepolyamines have been found to form stable metallic complexes. However, this mechanism is somewhat negatived by the fact that neither the betadiketones nor the N,Ndi(orthohydroxyarylmethylidene)alkylenepolyamines disclosed herein as such is capable of inhibiting'formation of deposits in both the heat exchange section, or fuel conduit section, of the fuel supply system and in the fuel inlet orifices in the combustion zone of aviation turbine engines. Although the exact functioning of the respective classes of compounds disclosed herein is not known, available experimental data clearly indicate that the respective classes of compounds disclosed herein coact with one another, as it has been found that deposits in both the heat exchange sectionof the fuel supply line and the fuel inlet orifices of the combustion chambers of aviation turbine engines are not inhibited by combinations of N,N'-di- (orthohydroxyaryhnethylidene)alkylenepolyamines and other materials that alone are capable of inhibiting deposits in the fuel inlet orifices of the combustion chambers of aviation turbine engines.

The preparation of the beta-diketones and the N,N'- di(orthohydroxyarylmethylidene)alkylenepolyamines disclosed herein forms no part of this invention. Thus, the N,N' di(orthohydroxyarylmethylidene)alkylenepolyamines can be prepared conveniently in known fashion by condensation of an aromatic aldehyde with an alkylenepolyamine in molar proportions of 2:1, respectively. The beta-diketones disclosed herein can be prepared as described in copending application Serial No. 783,730, filed in the name of Robert J. Hartle, now U.S. Patent No. 3,004,070, which application is directed to the betadiketones as such. Briefly, that application discloses that the beta-diketones can be prepared by condensation of a suitable disubstituted ketene dimer or codimer, in the presence of a Friedel-Crafts catalyst, with an equiva lent proportion of a suitable aromatic hydrocarbon.

The beta-diketones and the N,N-di(orthohydroxyarylmethylidene)alkylenepolyamines disclosed herein can be incorporated in aviation turbine fuels in any suitable manner. For example, they can be added singly or in combination, either as such, or in diluted form to the aviation turbine fuels either promptly after distillation of the latter or after storage of the fuels. Alternatively, the addition agents disclosed herein can be added to aviation turbine fuels in admixture with other addition agents adapted to improve one or more characteristics of the fuels. For example, the addition agents disclosed herein can be added to the fuels in admixture with corrosion inhibitors, such as amine salts of organic orthophosphates, antioxidants such as 2,6-ditertiarybutyl-4- methylphenol, or 2,4-dimethyl-6-tertiarybutylphenol.

The addition agents disclosed herein can be employed in aviation turbine fuels in any proportions sufficient to improve the thermal stability of the fuels. Normally a noticeable improvement in thermal stability will be obtained by the use of as little as five pounds of beta-diketone per thousand barrels of aviation turbine fuel and as little as five pounds of N,N'-(orthohydroxyarylmethylidene)alkylenepolyamines per thousand barrels of the fuel, but it is usually desirable to employ at least seven pounds per thousand barrels of fuel of the respective additives in order to obtain a substantial improvement in thermal stability. A major improvement will ordinarily be obtained by the use of proportions in the range of about 10 to 20 pounds per thousand barrels of the respective addition agents and accordingly such proportions are preferred. Normally it is not necessary to exceed 20 pounds per thousand barrels of fuel but in instances of aviation turbine fuels having very poor thermal stability characteristics, or in instances of relatively less effective members of the respective classes of addition agents disclosed herein, the agents can be employed in proportions of as much as 50 to 250 pounds or more per thousand barrels of fuel.

Aviation turbine fuels of the type whose use is included by this invention are liquid hydrocarbon mixtures whose properties are defined fully in the following specificationsz. MIL-J-5161E (Referee JP-4 Fuel), MIL-J-5624D (JP-4, JP-S Fuel), MIL-F-25656 (JP-6 Fuel), MIL-F-25524A, MIL-F-25558B (RJ-l Fuel), MIL-F-25576A (RP-1 Fuel), and American Airlines Spec. No. M6-4A. In general, typical aviation turbine fuels are characterized by the following common properties.

.Inspections:

Gravity, API 32.5-57. Existent gum, mg./ 100 ml.

(max) -7.

4 Potential gum, mg./ 100 ml.

(max) 4-14. Sulfur, percent (max.) 0.07-0.04. Mercaptan sulfur, percent (max.) 0.00l-0.005. Freezing point, F. (max.) 75 to 40.

Thermal value, B.t.u./lb.

(min.) 18,300-l8,500. Aniline-gravity constant 4500, usually 5250. Aromatics, vol. percent (max) 5-25.

Olefins, vol. percent (max.) 1-5.

The ability of the combinations of beta-diketones and orthohydroxyarylmethylidene substituted alkylenepolyamines disclosed herein to reduce formation of solid deposits in aviation turbine fuels at high service temperatures has been demonstrated by subjecting fuel compositions of the kind disclosed herein to the CFR Fuel Coker test procedure. This test procedure is described in detail in the Manual of ASTM Standards on Petroleum Products and Lubricants for 1957, Appendix XV. In accordance with this test method, aviation turbine fuels are subjected to flow conditions and temperature stresses similar to those in jet aircraft engines.

schematically, the test apparatus comprises a fuel system containing two heated section: (1) a preheater section that simulates the hot fuel line sections of a jet engine as typified by an engine fuel-lubricating oil cooler and (2) a filter section which simulates the nozzle, or fuel inlet, area of the combustion zone of a jet engine where fuel degradation particles may be trapped. A pre: cision sintered stainless steel filter is employed in the filter section to trap fuel degradation particles formed during the test. The extent of the build-up of fuel degradation particles in the filter section is indicated by the pressure differential across the test filter and is used as an index of the high temperature stability of the aviation turbine fuel. The extent of deposit formation in the preheater section is determined by inspection and is used as an index of the high temperature stability of the aviation turbine fuel in the hot fuel line section, or heat exchange section, of an aviation turbine engine. Preheater deposits are rated according to the following scale: 0=no visible deposits; l=visible haze or dulling, but no visible color; 2=barely visible discoloration; 3=light tan to peacock stain; 4=heavier than 3. In carrying out the test, the temperature of the fuel at the outlet of the preheater section is maintained at 400 F. and the filter section temperature is maintained at 500 F. During the test, fuel is caused to flow through the test apparatus at the rate of six pounds per hour and the test duration is five hours.

In the particular test reported below the test fuel, hereinafter referred to as Aviation Turbine Fuel A, was a blend of straight run distillates having the following characteristics.

Gravity, API 43.3 Freezing point, F. 60 Sulfur, l., percent 0.058 Mercaptan sulfur, percent 0.001 Existent gum, mg./ 100 ml. 0.5 Potential gum, mg./100 ml. 3.4 Aromatics, vol. percent 16.2 Olefins, vol. percent 1.5 Thermal value, B.t.u./lb. 18,576 Aniline gravity constant 6,343 Distillation:

Over point, F. 335 End point, F. 532 \10% evap. at F. 368 50% evap. at F. 418 evap. at F. 486 evap. at F. 518

Table of In. Hg, Minutes 127 300 10 300 Time to Reach a Pressure Drop of 25 In. Hg, Minutes 163 300 300 AP at 300 Minutes, In. Hg 25. 0 0. 0.10 Maximum Preheater Deposit Rating 3 4 0 0 Average Preheater Deposit Rat- From the results set forth in the preceding table, it is apparent that neither beta-diketones nor ,N,N' -d1- (orthohydroxyarylmethylidene)alkylenepolyamines of the classes disclosed herein are capable of inhibiting deposit formation in both the hot fuel line section and the fuel nozzles of an aviation turbine engine, In fact, as shown by the foregoing data, although the betadiketones are excellent inhibitors of filter deposits (fuel nozzle deposits), they tend to promote preheater deposits (hot fuel line deposits). Similarly, although the N,N' di(orthohydroxyarylmethylidene)alkylenepolyamines are excellent inhibitors of preheater deposits, they tend to promote filter deposits. As also shown by the foregoing data, when a combination of the materials is employed, each material modifies the undesirable characteristics of the other without diminishment of its own desirable characteristics.

It will be understood that the invention is not limited to the particular beta-diketone and N,N'-di(orthohydroxyarylmethylidene)alkylenepolyamine set forth in the specific preceding embodiment, and that other materials disclosed herein can also be employed with good results. For example, there can be substituted for the beta-diketone in the foregoing specific embodiment, in proportions of, for example, 10 or 20 pounds per thousand barrels of fuel,

l tolyl-2-o-ctyl-1,3-hexadecanedione, 1-xylyl-2-decyl-l,3-tetradecanedione, l-tolyl-2-decyl-1,3-hexadecanedione, and 1-tolyl-2-hexadecadienyl-1,3-tettadecanedione.

Similarly for the N,N'-di(orthohydroxyarylmethylidene) alkylenepolyamine of the foregoing specific embodiment, there can be substituted in proportions of 10 to 20 pounds per thousand barrels of fuel any of N,N'-di (2-hydroxy-6-methylbenzylidene) -2, 3

butylenediamine,

N,N-di (orthohydroxynaphthylidene) -1,3

propylenediamine,

N,N'-di (2-hydroXy-3 -methoxybenzylidene) -3 ,4-

diaminohexane, I

N,N-di (2-hydroxy-5 -chlorob enzylidene) -1,2- propylenediamine, Y

N,N'-di 2-hydroxy-3 -cyanob enzylidene) ethylenediamine,

N,N'-'di 2-hydroXy-3-ca1 b oxylb enzylidene) ethylenediamine, and

N,N-disalicylidenediethylenetriamineh The aviation tunbine fuel compositions of this invention can contain various other addition agents adapted to improve one or more properties of the fuel. For example, the fuel compositions of this invention can contain in addition to the addition agents disclosed herein, corrosion inhibitors, freezing point depressants, antioxidants, other metal deactivators and the like.

Many modifications and variations of the invention as herein described will suggest themselves to those skilled in the art, and resort may be had to such modifications and variations without departing from the spirit and scope of the invention. Accordingly, only such limitations should be imposed as are indicated in the claims appended hereto.

I claim:

1. A combustion gas turbine fuel composition comprising a major amount of a normally thermally unstable, liquid hydrocarbon aviation turbine fuel and a small amount, suiiicient to improve the thermal stability of said fuel of a combination of (a) an N,N-di(orthohydroxyarylmethylidene) alkylenepolyamine containing 2 to 3 amino nitrogen atoms and whose alkylene groups contain 2 to 6 carbon atoms each, and (b) a beta-diketone having the general formula:

where R is an aromatic hydrocarbon group having a nuclear carbon atom thereof connected directly to the adjacent carbonyl carbon atom and containing 6 to 22 carbon atoms, and R and R are acyclic aliphatic hydrocarbon radicals that contain 8 to 22 carbon atoms, said small amount comprising at least about five pounds of each member of said combination per thousand barrels of fuel,

2. The fuel composition of claim 1 where said small amount comprises about 5 to 250 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 10:1 to about 3. The fuel composition of claim 1 where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 4:1 to 1:4.

4. A combustion gas turbine fuel composition comprising a major amount of normally thermally unstable, liquid hydrocarbon aviation turbine fuel and a small amount, sufilcient to improve the thermal stability of said fuel of a combination of (a) an N,N'-di(orthohydroxyarylmethylidene)alkylenepolyamine containing 2 to 3 amino nitrogen atoms and Whose alkylene groups contain 2 to 6 carbon atoms each, and whose orthohydroxyaryl substituent is selected from the group consisting of unsubstituted orthohydroxyaryl radicals and orthohydroxyaryl radicals whose only substituents contain carbon and hydrogen atoms, and (b) a beta-diketone having the general formula:

Where R is a mononuclear hydrocarbon radical containing 6 to 20 carbon atoms and R and R" are alkyl groups containing 12 to 18 carbon atoms, said small amount corm prising at least about five pounds of each member of said combination per thousand barrels of fuel.

5. A combustion gas turbine fuel composition comprising a major amount of a normally thermally unstable, liquid hydrocarbon aviation turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of l-phenyl-Z-hexadecyl-1,3- eicosanedione, and N,N-disalicylidene-1,2-propylenediamine, said small amount comprising 5 to 250 pounds of each member of said combination per thousand barrels of fuel.

(References on following page) 7 References Cited in the file of this patent 2,316,012 2,533,205 UNITED STATES PATENTS 7 2,813,030

2,255,597 Downing et a1 Sept. 9, 1941 2,284,267 Downing et a1 May 26, 1942 5 487,745

3 Miller Apr. 6, 1943 Chenicek Dec. 12, 1950 Bartlett Nov. 12, 1957 FOREIGN PATENTS Great Britain June 20, 1935 

1. A COMBUSTION GAS TURBINE FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A NORMALLY THERMALLY UNSTABLE, LIQUID HYDROCARBON AVIATION TURBINE FUEL AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE THERMAL STABILITY OF SAID FUEL OF A COMBINATION OF (A) AN N,N''-DI(ORTHOHYDROXYARYLMETHYLIDENE)ALKYLENEPOLYAMINE FCONTAINING 2 TO 3 AMINO NITROGEN ATOMS AND WHOSE ALKYLENE GROUPS CONTAIN 2 TO 6 CARBON ATOMS EACH, AND (B) A BETA-DIKETONE HAVING THE GENERAL FORMULA: 